GRS 1716-249 is transitioning to the soft state.
ATel #10236; M. Armas Padilla, T. Munoz-Darias (IAC-Tenerife)
on 2 Apr 2017; 16:21 UT
Credential Certification: Montserrat Armas Padilla (email@example.com)
Subjects: X-ray, Binary, Black Hole, Transient
We report on the transition towards the soft state of the black hole candidate GRS 1716-249 (Nova Oph 93) currently in outburst (ATel #10196, ATel #10069, ATel #10036, ATel #9895).
The first 25 outburst observations obtained with Swift/XRT over the last two months showed the source stable in the hard state with an average 0.5-10 keV X-ray flux of ~ (5-6) x10 -9 erg cm -2 s -1 , photon indices in the range of 1.60-1.68 (using an absorbed power-law model to fit the spectra) and hardness ratio (HR; counts 2-10keV/counts 0.5-2keV) in the range 0.97-1.09.
Contrastingly, the last two Swift/XRT pointings (March 27 and April 2, 2017) indicate that the source is transitioning to the soft state. The power law photon index has softened (1.77+/-0.02 and 1.85+/-0.02, respectively) and the HR has evolved to values of 0.891 +/- 0.006 and 0.798 +/- 0.006, respectively (see attached Figure).